The post-translational processing of B-domain deleted blood coagulation factor eight (BDD-FVIII) is complex and requires von Willebrand factor (vWF) for efficient secretion. The candidate proposes to co-express BDD-FVIII and vWF in muscle cells by transfection of Cl C12 myocytes and to perform assays on the conditioned media and the cells to assess secretory efficacy. A helper-dependent adenoviral vector (HDV) system has been developed that has a large carrying capacity, low toxicity, long term expression and can accommodate an effective promoter as well as other transgenes in addition to BDD-FVIII. This HDV system will be used to co-express vWF and BDD-FVIII in mice via direct intramuscular injection. Studies of these transformed mice will include clotting activity of secreted BDD-FVIII, serum levels of vWF, and antibody response to the vector, FVIII and vWF. Muscle biopsies will be analyzed by H&E staining, immuunohistofluoresence, X-gal staining and northern analysis for BDD-FVIII and vWF mRNA. Achievement of efficient FVIII secretion from direct gene delivery into muscle will allow for a safer avenue to pursue in vivo gene therapy of hemophilia A in animal models and eventually in human patients.